Method and controller for an electric motor with fault detection

ABSTRACT

For each phase of a controller, semiconductor switches comprise a high side switch and a low side switch. A direct current voltage bus provides electrical energy to the semiconductor switches. A measuring circuit is adapted to measure the collector-emitter voltage or drain-source voltage for each semiconductor switch of the controller. A data processor determines that a short circuit in a particular semiconductor switch is present if the measured collector-emitter voltage or measured source-drain voltage for the particular semiconductor switch is lower than a minimum threshold and if an observed current associated with the particular semiconductor switch has an opposite polarity from a normal operational polarity. A driver simultaneously activates counterpart switches of like direct current input polarity that are coupled to other phase windings of the electric motor, other than the particular semiconductor switch, to protect the electric motor from potential damage associated with asymmetric current flow.

FIELD OF THE INVENTION

This invention relates to a method and controller for electric motorwith fault detection.

BACKGROUND OF THE INVENTION

An electric motor may feature a rotor with permanent magnets and astator, such as an interior permanent magnet (IPM) motor or an IPMsynchronous motor. In accordance with certain prior art, an inverter ormotor controller comprises semiconductor switches that support theprovision of alternating current outputs for one or more phases of theelectric motor. A short circuit, which appears across the outputterminals of one semiconductor switch, may cause an asymmetric currentto flow in the windings of an electric motor. The asymmetric currentmakes the motor susceptible to damage, such as demagnetization of one ormore permanent magnets within the motor (e.g., or its rotor). Thus,there is a need for an improved method and controller for an electricmotor with fault detection.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a method and system is presented forfault detection or prevention in a controller for an electric motor. Foreach phase of a controller, a pair of semiconductor switches comprises ahigh side switch and a low side switch. A direct current voltage busprovides electrical energy to the semiconductor switches (e.g.,switchably via a direct current power switch). A measuring circuit isadapted to measure the collector-emitter voltage or drain-source voltagefor each semiconductor switch of the controller. A data processordetermines that a short circuit in a particular semiconductor switch ispresent if the measured collector-emitter voltage or measuredsource-drain voltage for the particular semiconductor switch is lowerthan a minimum threshold (e.g., during a commanded off-state of theparticular semiconductor switch or over at least one complete cycle orwaveform of an inverter driver signal) and if an observed currentassociated with the particular semiconductor switch has an oppositepolarity from a normal operational polarity. A driver simultaneouslyactivates counterpart switches of like direct current input polaritythat are coupled to other phase windings of the electric motor, otherthan the particular semiconductor switch, to protect the electric motorfrom potential damage associated with asymmetric current flow (e.g.,prevent demagnetization of the permanent magnets in the electric motor).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of method and controller forelectric motor with fault detection.

FIG. 2 is a block diagram of another embodiment of method and controllerfor electric motor with fault detection.

FIG. 3 is a flow chart of a first embodiment of a method for controllingan electrical motor with fault detection.

FIG. 4 is a flow chart of a second embodiment of a method forcontrolling an electrical motor with fault detection.

FIG. 5 is a flow chart of a third embodiment of a method for controllingan electrical motor with fault detection.

FIG. 6 is a flow chart of a fourth embodiment of a method forcontrolling an electrical motor with fault detection.

FIG. 7 is a flow chart of a fifth embodiment of a method for controllingan electrical motor with fault detection.

FIG. 8 is a flow chart of a sixth embodiment of a method for controllingan electrical motor with fault detection.

FIG. 9 is an illustrative table of voltage states of semiconductorswitches, corresponding output current for phase output nodes,corresponding faults detected, and corresponding corrective actions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An asymmetric current flow in the windings (44, 46, and 48) of a motor45 refer to a condition where a direct current (e.g., positive currentor negative current) or direct current offset from one or more directcurrent terminals (64, 66) is continuously applied to only one winding(44, 46, or 48) or one phase of the motor 45. The asymmetric currentflow may be referred to as an unbalanced current flow. For example, theasymmetric current flow may result from a fault or short circuit in asingle semiconductor switch of an inverter or controller. For certainmotor 45 designs, an asymmetric current flow or unbalanced current flowmay place the one or more motor windings (44, 46, or 48) under thermalstress, may partially demagnetize permanent magnets of the motor 45 overan extended period of time, or may make the motor 45 susceptible toreduced longevity, among other things. For example, the continuous inputof direct current or a direct current offset to a winding (44, 46, or48) can result in thermal stress or damage to the winding (44, 46, or48) that is typically rated or designed for alternating current input,or the discontinuous input of electrical energy. Further, because onephase winding (44, 46, or 48) has a direct current offset from the otherphase windings that is not coordinated with the frequency of thealternating current applied to the other phases, the direct currentoffset can damage the motor 45 or electrical machine, or demagnetize itspermanent magnets over time.

In accordance with one embodiment, FIG. 1 discloses a system, inverteror controller 11 for controlling an electric motor 45, where thecontroller 11 is capable of fault detection and prevention measures. Theelectric motor 45 may comprise an interior permanent magnet (IPM) motor45 or another alternating current machine. As illustrated, the system,aside from the motor 45, may be referred to as an inverter or a motorcontroller 11 with fault detection.

In FIG. 1, the data processor 10 is coupled to a driver 12. The driver12 comprises a semiconductor drive circuit that drives or controlssemiconductor switches (81, 82, 181, 182, 281, or 282) to generatecontrol signals for an inverter circuit. The inverter circuit (80, 180and 280) converts a direct current input signal from a direct currentbus (64, 66) to one or more alternating current output signals at outputterminals (24, 124, and 224). The direct current bus (64, 66) provideselectric energy to the controller or inverter, including itssemiconductor switches. In turn, the inverter circuit is coupled to themotor 45 or motor windings (44, 46, and 48). Although the motor windings(44, 46, and 48) are illustrated as Wye (Y) fed configuration forillustrative purposes with a central ground connection 49, otherarrangements are possible and fall within the scope of the claims.

In FIG. 1, the semiconductor switches (81, 82, 181, 182, 281, or 282)for the multiple phases (e.g., first phase 80, second phase 180 andthird phase 280) collectively form an inverter circuit in which directcurrent inputted to the inverter circuit is inverted or transformed intoone or more alternating current output signals for application to acorresponding phase or winding (44, 46, or 48) of the electric motor 45.

The inverter circuit comprises power electronics, such as switchingsemiconductors (81, 82, 181, 182, 281, or 282) to generate, modify andcontrol pulse-width modulated signals or other alternating currentsignals (e.g., pulse, square wave, sinusoidal, or other waveforms)applied to the motor 45. An output stage of the inverter circuitprovides a pulse-width modulated signal or other alternating currentsignal for control of the motor 45.

For each output phase (80, 180, and 280), the controller 11 or invertercomprises a pair of semiconductor switches (81, 82, 181, 182, 281, or282). In one embodiment, the semiconductor switches (81, 82, 181, 182,281, or 282) may comprise insulated gate bipolar transistors (IGBT),field effect transistors, power transistors, or other semiconductordevices.

First, the controller 11 or inverter comprises a first pair ofsemiconductor switches (81, 82) including a high side switch (81) and alow side switch (82) for a first phase 80 of the controller 11. In thefirst phase 80, the high side switch (81) may be referred to as a highside switch because one of its switched output terminals (e.g.,collector 14 or drain, among output terminals (14, 24)) may be connectedto a positive direct current terminal 64 of the direct current bus. Thelow side switch (82) may be referred to as a low side switch because oneof its switched output terminals (e.g., emitter 26 or source, amongoutput terminals (16, 26)) may be connected to a negative direct currentterminal 66 of the direct current bus.

Second, the controller 11 or inverter comprises a second pair ofsemiconductor switches (181, 182) including a high side switch (181) anda low side switch (182) for a second phase (180) of the controller. Inthe second phase 180, the high side switch (181) may be referred to as ahigh side switch because one of its switched output terminals (e.g.,collector 114 or drain, among output terminals (114, 124)) may beconnected to a positive direct current terminal 64 of the direct currentbus. The low side switch (182) may be referred to as a low side switchbecause one of its switched output terminals (e.g., emitter 126 orsource, among output terminals (116, 126)) may be connected to anegative direct current terminal 66 of the direct current bus.

Third, the controller or inverter comprises a third pair ofsemiconductor switches including a high side switch and a low sideswitch for a second phase of the controller. In the third phase 280, thehigh side switch (281) may be referred to as a high side switch becauseone of its switched output terminals (e.g., collector 214 or drain,among output terminals (214, 224)) may be connected to a positive directcurrent terminal 64 of the direct current bus. The low side switch (282)may be referred to as a low side switch because one of its switchedoutput terminals (e.g., emitter 226 or source, among output terminals(216, 226)) may be connected to a negative direct current terminal 66 ofthe direct current bus.

Although FIG. 1 and FIG. 2 each illustrate a three-phase controller forcontrolling an electric motor 45, a controller may generally have one ormore phases and a controller with two or more phases may be used topractice any embodiment of this disclosure.

In one embodiment, the inverter circuit, inverter or controller 11 ispowered by a direct current (DC) voltage bus (64, 66, collectively). Forexample, in FIG. 1 a direct current voltage bus (64, 66) is coupled tocollector and emitter terminals or source and drain terminals of thesemiconductor switches (81, 82, 181, 182, 281, or 282) for each phase.The input terminal (18, 20, 118, 120, 218, and 220) of eachsemiconductor switch (81, 82, 181, 182, 281, or 282) is coupled to thedriver 12. The input terminal (18, 20, 118, 120, 218, and 220) of eachsemiconductor switch may comprise a gate or a base, for example. Theoutput terminal (24, 124, 224) of each semiconductor switch is coupledto a terminal of a motor winding (44, 46, or 48). The output terminal(24, 124, 224) of each phase may be located at the junction of the highside switch and the low side switch for a particular phase. Eachdifferent phase (80, 180, 280) of the motor 45 may be associated with acorresponding motor 45 winding (44, 46, or 48).

As shown in FIG. 1, a protecting diode (28, 30) may be coupled betweenthe collector and emitter (or the source and drain) of eachsemiconductor switch (81, 82, 181, 182, 281, or 282) to limit thecurrent flowing in between the collector and emitter (or outputterminals) during transient states in which the semiconductor switch isdeactivated or activated.

A measuring circuit or voltage sensor (32, 34) is coupled between thecollector and emitter terminals or the source and drain terminals of thesemiconductor switches (81, 82, 181, 182, 281, or 282) for each phase(80, 180, 280). Each voltage sensor (32, 34) is adapted to measure thecollector-emitter voltage or source-drain voltage for each semiconductorswitch of the controller 11. If the detected collector-emitter voltageor source-drain voltage for an inactive (e.g., switched off)semiconductor switch (81, 82, 181, 182, 281, or 282) is less than athreshold voltage level, the semiconductor device (81, 82, 181, 182,281, or 282) may have a short circuit or a greater than typical leakagecurrent, which potentially indicates an imminent short circuit failuremode of the semiconductor device. The data processor 10 may use theoutput of one or more voltage sensors (32, 34) to estimate the currentflowing within a respective winding (44, 46, or 48) for a correspondingphase of the inverter or controller 11.

Each voltage sensor (32, 34) or measuring circuit provides a high inputimpedance relative to the semiconductor switch (81, 82, 181, 182, 281,or 282) and the motor winding (44, 46, or 48) such that the voltagesensor (32, 34) or the measuring circuit does not perturb theperformance of the semiconductor switch or draw material current (e.g.,emitter current or collector current) from the semiconductor switch orthe winding (44, 46, or 48). In one embodiment, the voltage sensor (32,34) or the measuring circuit may comprise a high impedance voltage meteror voltage sensor. For example, the measuring circuit may comprise ahigh impedance voltage sensor that uses one or more operationalamplifiers for comparison of an input voltage to a reference voltage.The reference voltage may be provided by a battery, a voltage regulator,or a Zener diode, for example. In one configuration, the output of thevoltage sensor may be coupled to an analog-to-digital converter toprovide a suitable digital input for the data processor 10.

The measuring circuit or voltage sensor (32, 34) may provide an analogoutput or a digital output. As shown in FIG. 1 each voltage sensor (32,34) is coupled to the data processor 10 to provide a digital outputthereto. If the voltage sensor (32, 34) or measuring circuit provides ananalog output, an analog-to-digital converter may be interposed betweenthe voltage sensor (32, 34) and the inputs of the data processor 10. Themeasuring circuit or voltage sensor (32, 34) is capable of detectinggreater than normal leakage current when the semiconductor switch (81,82, 181, 182, 281, or 282) is deactivated or turned off. Accordingly,the measuring circuit or voltage sensor is well suited for providing anearly warning of a later complete fault or short circuit in thesemiconductor switch or protecting diode (28, 30), such that currentinitially associated with the early detected short circuit or fault maybe insufficient to damage the motor 45 or electrical machine. In somecases, the data processor 10 may lower (e.g., slightly, but withsuitable bias to activate or turn on the switch) the input voltage tothe gate or base input of the semiconductor switch (82, 181, 182, 281,or 282) with a greater than typical or normal leakage current to ensurethe semiconductor device is operating within a desired operational zonethat minimizes any fault or short circuit current in the switched outputterminals of the semiconductor device.

In one configuration, current sensors (59, 159, 259) are coupled tocorresponding terminals (24, 124, 224) of the respective phase outputnodes. Each current sensor (59, 159, 259) measures or senses currentmagnitude at the phase output node, the polarity (e.g., sense ordirection) of the current flowing at the phase output node, or both(collectively or individually “measured current”). If the current sensor(59, 159, 259) provides an analog output of the measured current, theanalog output of each current sensor (59, 159, 259) is coupled to ananalog-to-digital converter 255 that is interposed between the currentsensor output and the data processor 10. Here, the connections betweenthe analog-to-digital converter 255 and the current sensors (59, 159,259) are illustrated by the mating pairs of arrows with common referenceletters, A, B, and C in FIG. 1. However, if the current sensor (59, 159,259) provides a digital output of the measured current in an alternateembodiment, the analog-to-digital converter 255 can be omitted, wherethe current sensor output is connected directly to the data processor10, or via buffer memory.

Each current sensor (59, 159 and 259) provides an indicator (e.g.,current polarity indicator, current magnitude, or both) of the measuredcurrent indicative of whether or not the measured or observed phaseoutput node current (associated with a motor winding (e.g., 44, 46, 48)coupled to the particular semiconductor switch) has an opposite polarityfrom a normal operational polarity. The observed current polarity may bedifferent or opposite from the normal operational polarity if any of thesemiconductor switches or diodes (28, 30) fails as a short circuit orbreaks down from the flow of reverse current or current of oppositepolarity to the normal current, for example.

Although one current sensor (59, 159, 259) per phase output node (e.g.,24, 124, 224) is shown in FIG. 1, in an alternate embodiment the totalnumber of current sensors may be limited to N−1, where N is equal to thenumber of phases of the electric motor 45. In such an alternateembodiment, the data processor 10 is adapted to estimate or calculatethe observed current in the phase output node (e.g., terminal 24)without a sensor from the other output nodes with sensors (e.g., twocurrent sensors 59, 159) in accordance with electrical network analysis,such as Kirchhoffs law.

The driver 12 provides digital signals for activating the semiconductorswitches (82, 181, 182, 281, or 282) in accordance with a desired inputsignal or control signals from the data processor 10. For example,during operation of the motor 45 in an operational mode, the inputsignal may comprise a sinusoidal signal, a square wave signal or anothersignal. During a diagnostic mode or a test mode, the input signal mayprovide input signals or control signals to selectively activate one ormore of the semiconductor switches (82, 181, 182, 281, or 282) toprevent damage to motor winding (44, 46, or 48)s or permanent magnets ofthe motor 45.

In one embodiment, the data processor 10 may comprise an electronic dataprocessor, a microprocessor, a microcontroller, a programmable logicarray, a logic circuit, an arithmetic logic unit, an applicationspecific integrated circuit, a digital signal processor, aproportional-integral-derivative (PID) controller, or another dataprocessing device. Further, the data processor 10 may be coupled to adata storage device 67 via a data bus 69.

The data storage device 67 may comprise electronic memory, nonvolatilerandom access memory, an optical storage device, a magnetic storagedevice, a hard disk drive, an optical disc drive, or another device forstoring digital data or analog data. The data storage device 67 maystore a look-up table, data base, file, inverted file, or another datastructure with voltage threshold levels that indicate a short circuit orfault in a semiconductor switch (82, 181, 182, 281, or 282) andcorresponding switch states to be activated in the event of a fault orshort circuit of a particular semiconductor switch (82, 181, 182, 281,or 282).

In one illustrative example, the data processor 10 determines that ashort circuit in a particular semiconductor switch is present if themeasured collector-emitter voltage or measured source-drain voltage forthe particular semiconductor switch is lower than a minimum threshold(e.g., over at least one complete cycle or waveform of an inverterdriver 12 signal) or approaches zero volts over a sampling period. If afault or short is detected in the particular semiconductor switch, adriver 12, or logic control circuit therein, simultaneously activatescounterpart switches of like direct current input polarity (e.g., alllow side switches (82, 182, 282) or all high side switches (81, 181,281)) that are coupled to other phase windings (44, 46, or 48) of theelectric motor 45, other than the particular semiconductor switch toprevent damage to the motor 45, such as the motor windings (44, 46, or48) or demagnetization of the permanent magnets in the electric motor45. For example, switches (e.g., counterpart switches) of like directcurrent input polarity means semiconductor switches that are connectedto the direct current bus in the same manner or a substantially similarmanner with respect to their output terminals (e.g., collector andemitter terminals of transistors with same junction materials biased inthe same general manner and with the same polarity).

In one example of executing a protective measure to prevent damage tothe motor 45, the data processor 10 instructs the driver 12 tosimultaneously activate (e.g., turn on) all high side semiconductorswitches for each phase if the data processor 10 detects a short orfault in one high side semiconductor switch via sensor data from thevoltage sensor (32, 34). Conversely, in another example, the dataprocessor 10 instructs the driver 12 to simultaneously activate (e.g.,turn on) all low side semiconductor switches for each phase if the dataprocessor 10 detects a short or fault in one low side semiconductorswitch. The data processor 10 may keep the simultaneously activation ofthe semiconductor switches (e.g., high side switches or low sideswitches) until the direct current bus is switched off, deactivated, orless than a threshold voltage level (e.g., 60 Volts direct current),where the threshold voltage level is a motor 45-dependent ormachine-dependent variable that is selected to avoid damage to the motor45. Further, the data processor 10 may keep the activation of thecounterpart switches of like direct current input polarity, until thepower to the inverter is recycled, or until the direct current powerswitch 29 is cycled off and on at least once.

FIG. 2 illustrates an alternative embodiment of a controller 111 orinverter with fault detection for controlling an electric motor 45. Forexample, the controller 11 or inverter of FIG. 2 is well suited forcontrolling a switched reluctance motor 15. The controller 111 orinverter of FIG. 2 is different from FIG. 1 because of variousmodifications that facilitate control of a switched reluctance motor 15.For example, the inverter circuit (53, 153 and 253 collectively) of FIG.2 features additional diodes (31, 45, 55) and does not have an outputthat is formed by connection of the output terminals of a low sidesemiconductor switch and a high side semiconductor switch. Further, thecontroller 111 of FIG. 2 has current a rotor or shaft position sensor17, and one or more winding temperature sensors 19, among other things.Like reference numbers in FIG. 1 and FIG. 2 indicate like elements.

In FIG. 2, the data processor 10 is coupled to a driver 12. The driver12 comprises a semiconductor drive circuit that drives or controlsswitching semiconductors (35, 37, 135, 137, 235, 237) to generatecontrol signals for each phase (e.g., 53, 153, 253) of an invertercircuit. As illustrated, the inverter circuit comprises the circuitryand semiconductor switches (35, 37, 135, 137, 235, 237) associated witha first phase 53 (“Phase A”), a second phase 153 (“Phase B”) and a thirdphase 253 (“Phase C”). The inverter circuit converts a direct currentinput signal from a direct current bus (64, 66 collectively) to one ormore alternating current output signals for output at output terminals(39, 43, 139, 143, 239, and 243). In turn, the inverter circuit iscoupled to the motor 15 or motor windings (21, 22 and 23). Thecontroller 111 of FIG. 2 comprises a controller for a switchedreluctance motor 15 with three separate windings (21, 22, and 23) forthree corresponding phases: Phase A, Phase B and Phase C.

In FIG. 2, the semiconductor switches (35, 37, 135, 137, 235, 237),protecting diodes (28, 30), supplemental diodes (31, 45, 55, 131, 145,155), voltage sensors (32, 34) for the multiple phases (53, 153, 253)collectively form an inverter circuit in which direct current voltageinputted to the inverter circuit is inverted or transformed into one ormore alternating current output signals for application to acorresponding phase or winding (21, 22, or 23) of the electric motor 15.The inverter circuit comprises power electronics, such as switchingsemiconductors (35, 37, 135, 137, 235, 237) to generate, modify andcontrol pulse-width modulated signals or other alternating currentsignals (e.g., pulse, square wave, sinusoidal, or other waveforms)applied to the motor 15. An output stage of the inverter circuitprovides a pulse-width modulated signal or other alternating currentsignal for control of the motor 15.

For each output phase (53, 153, 253) the controller 111 or invertercomprises a pair of semiconductor switches (e.g., a first pair 35, 37; asecond pair 135, 137, and a third pair 235, 237). Each semiconductorswitch (35, 37, 135, 137, 235, 237) may comprise an insulated gatebipolar transistor (IGBT), a field effect transistor, a powertransistor, or another semiconductor device.

First, in the first phase 53 (“Phase A”) the controller 111 or invertercomprises a first pair of semiconductor switches (35, 37) including ahigh side switch 35 with its output terminals (33, 39) coupled in serieswith a low side diode 131 and a low side switch 37 with its outputterminals (43, 47) coupled in series with a high side diode 31 for thefirst phase 53 of the controller 111. For the first phase 53, a highside semiconductor switch 35 has its output terminals (33, 39) coupledin parallel with a protecting diode 28 and a voltage sensor 32, whereasa low side semiconductor switch 37 has its output terminals (43, 47)coupled in parallel with a protecting diode 30 and voltage sensor 34.

Second, in the second phase 153 (“Phase B”) the controller 111 orinverter comprises a first pair of semiconductor switches (135, 137)including a high side switch 135 with its output terminals (133, 139)coupled in series with a low side diode 145 and a low side switch 137with its output terminals (143, 147) coupled in series with a high sidediode 45 for the second phase 153 of the controller 111. For the secondphase 153, a high side semiconductor switch 135 has its output terminals(133, 139) coupled in parallel with a protecting diode 28 and a voltagesensor 32, whereas a low side semiconductor switch 137 has its outputterminals (143, 147) coupled in parallel with a protecting diode 30 andvoltage sensor 34.

Third, in the third phase 253 (“Phase C”) the controller 111 or invertercomprises a first pair of semiconductor switches (235, 237) including ahigh side switch 235 with its output terminals (233, 239) coupled inseries with a low side diode 155 and a low side switch 237 with itsoutput terminals (243, 247) coupled in series with a high side diode 55for the third phase 253 of the controller 111. For the third phase 253,a high side semiconductor switch 235 has its output terminals (233, 239)coupled in parallel with a protecting diode 28 and a voltage sensor 32,whereas a low side semiconductor switch 237 has its output terminals(243, 247) coupled in parallel with a protecting diode 30 and voltagesensor 34.

As used throughout this document, the output terminals comprisecontrolled or switched terminals, such as the collector and emitter of asemiconductor switch, or the drain and source of a field effecttransistor. Similarly, as used herein, the control terminals comprise abase of a transistor or gate of a field effect transistor. Although FIG.1 and FIG. 2 each illustrate a three-phase controller for controlling anelectric motor (45 or 15), a controller may generally have one or morephases and a controller with two or more phases may be used to practiceany embodiment of this disclosure.

In one embodiment, the inverter circuit or inverter is powered by adirect current (DC) voltage bus (64, 66 collectively). For example, inFIG. 2 a direct current voltage bus (64, 66) is coupled to collector andemitter terminals of each pair of semiconductor switches, or source anddrain terminals of the semiconductor switches for each phase. Acapacitor 13, such as an electrolytic capacitor may be coupled betweenthe voltage rails or terminals of the direct current voltage bus (64,66) to smooth or reduce ripple (e.g., an alternating current component)in the direct current or to otherwise filter the direct current.

The input terminal or control terminal (A1, A2, B1, B2, C1, C2) of eachsemiconductor switch (35, 37, 135, 137, 235, 237) is coupled to thedriver 12. The input terminal or control terminal of each semiconductorswitch (35, 37, 135, 137, 235, 237) may comprise a gate or a base, forexample. The output terminal of each semiconductor switch is coupled toa terminal of a motor 15 winding (21, 22, or 23). Each different phaseof the motor 15 may be associated with a corresponding motor winding(21, 22, or 23).

A first terminal of a first motor winding 21 (for Phase A) may becoupled to an emitter or output terminal 39 of the high sidesemiconductor switch 35 of the first phase 53 and second terminal of thewinding 21, opposite of the first terminal, may be coupled to acollector or output terminal 43 of a low side semiconductor switch 37 ofthe first phase 53. A first terminal of a second motor winding 22 (forPhase B) may be coupled to an emitter or output terminal 139 of the highside semiconductor switch 135 of the second phase 153 and secondterminal of the winding 22, opposite of the first terminal, may becoupled to a collector or output terminal 143 of a low sidesemiconductor switch 137 of the second phase 153. A first terminal of athird motor winding 23 (for Phase C) may be coupled to an emitter oroutput terminal 239 of the high side semiconductor switch 235 of thethird phase 253 and second terminal of the winding 23, opposite of thefirst terminal, may be coupled to a collector or output terminal 243 ofa low side semiconductor switch 237 of the third phase 253.

As shown in FIG. 2, a protecting diode (28, 30) may be coupled betweenthe collector and emitter (or the source and drain) of eachsemiconductor switch (35, 37, 135, 137, 235, 237) to limit the currentflowing in between the collector and emitter during transient states inwhich the semiconductor switch is deactivated (e.g., switched off) oractivated (e.g., switched on).

A high side voltage sensor 32 or measuring circuit is coupled betweenthe output terminals (33, 39, 133, 139, 233, 239) of each high sidesemiconductor switch, where the output terminals may comprise collectorand emitter terminals or the source and drain terminals of thesemiconductor switches for each phase (53, 153, 253). A low side voltagesensor 34 or measuring circuit is coupled between the output terminals(43, 47, 143, 147, 243, 247) of each high side semiconductor switch,where the output terminals may comprise collector and emitter terminalsor the source and drain terminals of the semiconductor switches for eachphase (53, 153, 253). The voltage sensors (32, 34) are adapted tomeasure the collector-emitter voltage or source-drain voltage for eachsemiconductor switch of the controller 111. Each high side voltagesensor 32 or measuring circuit provides a high input impedance relativeto the high side semiconductor switch (35, 135, 235) and the windingssuch that the voltage sensor 32 or measuring circuit does not perturbthe performance of the semiconductor switch or draw material current(e.g., emitter current or collector current) from the semiconductorswitch. Each low side voltage sensor 34 or measuring circuit provides ahigh input impedance relative to the low side semiconductor switch (37,137, 237) and the windings such that the voltage sensor 34 or measuringcircuit does not perturb the performance of the semiconductor switch ordraw material current (e.g., emitter current or collector current) fromthe semiconductor switch. In one embodiment, the voltage sensor (32, 34)or measuring circuit may comprise a high impedance voltage meter orvoltage sensor. For example, the measuring circuit may comprise a highimpedance voltage sensor that is uses one or more operational amplifiersfor comparison of an input voltage to a reference voltage.

The voltage sensor (32, 34) or measuring circuit may provide an analogoutput or a digital output. As shown in FIG. 2 each measuring circuit iscoupled to the data processor 10 to provide a digital output thereto. Ifthe voltage sensor (32, 34) measuring circuit provides an analog output,an analog-to-digital converter may be interposed between the voltagesensor (32, 34) and the inputs of the data processor 10.

The driver 12 provides digital signals for activating the semiconductorswitches (35, 37, 135, 137, 235, 237) in accordance with a desired inputsignal or control signals from the data processor 10. For example,during operation of the motor 15 in an operational mode, the inputsignal may comprise a sinusoidal signal, a square wave signal or anothersignal. During a diagnostic mode or a test mode, the input signal mayprovide input signals or control signals to selectively activate one ormore of the semiconductor switches (35, 37, 135, 137, 235, 237) toprevent damage to one or more motor windings (21, 22, 23) or one or morepermanent magnets of the motor 15.

A data processor 10 determines that a short circuit or fault in aparticular semiconductor switch (35, 37, 135, 137, 235, 237) is presentif the measured collector-emitter voltage or measured source-drainvoltage (by the voltage sensor (32, 34)) for the particularsemiconductor switch is lower than a minimum threshold (e.g., over atleast one complete cycle or waveform of an inverter driver 12 signal) orapproaches zero during a sampling period. A driver 12 or a logic controlcircuit simultaneously activates counterpart switches of like directcurrent input polarity that are coupled to other phase windings (21, 22,or 23) of the electric motor 15 than the particular semiconductor switch(35, 37, 135, 137, 235, 237) to prevent demagnetization of the permanentmagnets in the electric motor 15.

In FIG. 2, the motor 15 is associated with a position sensor 17 (e.g., aposition sensor, a resolver or encoder position sensor) that isassociated with the motor shaft or the rotor of the motor 15. Forexample, the position sensor 17 may comprise a magnetic field sensor(e.g., Hall Effect sensor) that detects a shaft or rotor position of amagnet secured to the shaft. The position sensor 17 provides positiondata, velocity data, or acceleration data for the shaft or rotor of themotor 15. The position data, velocity data or acceleration data can beprovided from the position sensor 17 to the data processor 10 (e.g., ina digital format or analog format). For example, the position sensor 17provides position data for a corresponding time instant to the dataprocessor 10.

In one configuration, the position sensor 17 may comprise one or more ofthe following: a direct current motor, an optical encoder, a magneticfield sensor (e.g., Hall Effect sensor), magneto-resistive sensor, and aresolver (e.g., a brushless resolver). The output of the sensor iscapable of communication with a position and speed processing module(e.g., electronic or software module) in the data processor 10. In oneembodiment, the sensor 17 may be coupled to an analog-to-digitalconverter (not shown) that converts analog position data or velocitydata to digital position or velocity data, respectively. In otherembodiments, the sensor (e.g., digital position encoder) may provide adigital data output of position data or velocity data for the motorshaft or rotor.

One or more current sensors (59, 159, 259) and one or more windingtemperature sensors 19 provide feedback data to the data processor 10for processing. For example, a current sensor (59, 159, 259) isassociated with each phase or winding (21, 22, 23) of the motor 15. Thecurrent sensor (59, 159, 259) provides feedback data (e.g., currentfeedback data or phase output node current, such as i_(a), i_(b), i_(c))among other possible feedback data or signals, for example. In FIG. 2,phase output node current is present at terminals (39, 139, 239, 43,143, 243), where a current sensor may be assigned to each terminal of amotor winding (21, 22, 23) or to each motor winding (21, 22, 23).

Although one current sensor (59, 159, 259) per phase output node or permotor winding (21, 22, 23) is shown in FIG. 1, in an alternateembodiment the total number of current sensors may be limited to N−1,where N is equal to the number of phases of the electric motor 15. Insuch an alternate embodiment, the data processor 10 is adapted toestimate or calculate the observed current in the phase output node(e.g., 39 or 43) without a sensor from the other output nodes withsensors (e.g., two current sensors 59, 159) in accordance withelectrical network analysis, such as Kirchhoffs law.

As illustrated in FIG. 2, one or more winding temperature sensors 19provide winding sensor measurements, winding temperature data, windingsensor data, or thermal data, thermal measurements or thermal signals tothe data processor 10 for processing. The temperature sensors 19 mayprovide temperature data or thermal data to rotor magnet temperatureestimation module in the data processor 10. In turn, the temperatureestimation module in the data processor 10 may scale or adjust one ormore outputs of the inverter to compensate for inefficiency or reducedperformance associated with thermal degradation.

Other possible feedback data includes, but is not limited to,semiconductor temperature readings of the inverter circuit, three phasevoltage data, or other thermal or performance information for the motor15.

The method of FIG. 3 begins in step S300.

In step S300, a voltage sensor (32, 34) or another measuring circuitmeasures the collector-emitter voltage or source-drain voltage for eachsemiconductor switch (e.g., 81, 82, 181, 182, 281, 282, 35, 37, 135,137, 235, 237) of a controller (11 or 111).

In step S302, a data processor 10 or logic circuit determines that ashort circuit in a particular semiconductor switch (e.g., 81, 82, 181,182, 281, 282, 35, 37, 135, 137, 235, 237) is present if the measuredcollector-emitter voltage or source-drain voltage for the particularsemiconductor switch is lower than a minimum threshold during acommanded off-state of the particular semiconductor switch (e.g., overat least one complete cycle or waveform of an inverter driver 12 signal)or approaches zero volts for a sampling period and if an observedcurrent associated with the particular semiconductor switch has anopposite polarity from a normal operational polarity. For example, instep S320, a data processor 10 or logic circuit determines that a shortcircuit in a particular semiconductor switch (e.g., 81, 82, 181, 182,281, 282; or 35, 37, 135, 137, 235, 237) is present if the measuredcollector-emitter voltage or source-drain voltage for the particularsemiconductor switch is lower than a minimum threshold during acommanded off-state of the particular semiconductor switch or approacheszero volts for a sampling period and if an observed phase output nodecurrent (associated with a motor winding (e.g., 44, 46, 48; or 21, 22,23) coupled to the particular semiconductor switch) has an oppositepolarity from a normal operational polarity.

In step S304, the data processor 10, the driver 12 or bothsimultaneously activate (e.g., turn on) counterpart switches of likedirect current (DC) input polarity that are coupled to other phasewindings (e.g., 44, 46, 48, 21, 22, 23) of the electric motor (e.g., 45or 15), other than the particular semiconductor switch, if the shortcircuit is determined to be present, to prevent damage to the motor,such as demagnetization of the permanent magnets in the electric motoror thermal damage to the windings of the motor. Step S304 may be carriedout by various techniques that may be applied alternately orcumulatively. Under a first technique, if the short circuit is detectedin a high side switch, then all other high side switches are activated.Under a second technique, if a short circuit is detected in a low sideswitch, then all other low side switches are activated. Under a thirdtechnique, if the data processor 10 detects a short circuit or fault ina high side switch from voltage readings of the voltage sensor 32, thenthe data processor 10 instructs the driver 12 to activate (e.g., turnon) one or more (e.g., all) other high side switches of the inverter (11or 111). Under a fourth technique, if the data processor 10 detects ashort circuit or fault in a low side switch from voltage readings of thevoltage sensor 34, then the data processor 10 instructs the driver 12 toactivate (e.g., turn on) one or more (e.g., all) other low side switchesof the inverter (11 or 111). Under a fifth technique, if the dataprocessor 10 detects a short circuit or fault in a high side switch fromvoltage readings of the voltage sensor 32, then the data processor 10instructs the driver 12 to activate (e.g., turn on) one or more (e.g.,all) other high side switches of the inverter (11 or 111), until thedirect current power switch 29 is cycled (e.g., deactivated andactivated in succession) as observed or directed by the data processor10. Under a sixth technique, if the data processor 10 detects a shortcircuit or fault in a low side switch from voltage readings of thevoltage sensor 34, then the data processor 10 instructs the driver 12 toactivate (e.g., turn on) one or more (e.g., all) other low side switchesof the inverter (11 or 111), until the direct current power switch 29 iscycled (e.g., deactivated and activated in succession) as observed orcommanded by the data processor 10.

The method of FIG. 4 is similar to the method of FIG. 3, except themethod of FIG. 4 further comprises step S306.

In step S306, the data processor 10 verifies that the short circuit ofthe particular switch is present where the particular semiconductorswitch (e.g., 81, 82, 181, 182, 281, 282, 35, 37, 135, 137, 235, 237)remains in a closed state where no bias voltage or quiescent state biasvoltage is provided to the base or gate of the semiconductor switch fromthe driver 12 or otherwise. For example, the data processor 10 and thedriver 12 removes the bias voltage from the base or gate of a particularsemiconductor switch (e.g., 81, 82, 181, 182, 281, 282, 35, 37, 135,137, 235, 237) and then the voltage sensor (32, 34) measures whether thevoltage drop across the output terminals (e.g., collector-emittervoltage (V_(CE))) of the switch is below a threshold minimum voltage, isminimal, or approaches zero volts for a sampling period.

The method of FIG. 5 is similar to the method of FIG. 3, except themethod of FIG. 5 further comprises step S308.

In step S308, the data processor 10 verifies that the short circuit ofthe particular semiconductor switch (e.g., 81, 82, 181, 182, 281, 282,35, 37, 135, 137, 235, 237) is present where the particularsemiconductor switch does not enter into an open state, indicated by acollector-emitter voltage or source-drain voltage exceeding a maximumthreshold, wherein no bias voltage or a quiescent state bias voltage isprovided to the base or gate of the semiconductor switch. For example,the switch does not enter the open state and has a short circuit if thedata processor 10 and the driver 12 removes the bias voltage from thebase or gate of a particular switch while the voltage sensor (32, 34)measures voltage drop across the output terminals of the switch, wherethe collector-emitter voltage or the source-drain voltage is less thanthe maximum threshold (e.g., where a greater than typical or normalleakage current (e.g., I_(C)) is flowing between the output terminals ofthe particular semiconductor switch). Conversely, during normaloperation, the switch enters the open state and does not have a shortcircuit if the data processor 10 and the driver 12 removes the biasvoltage from the base or gate of a particular switch while the voltagesensor (32, 34) measures voltage drop across the output terminals of theswitch, where the collector-emitter voltage or the source-drain voltageexceeds the maximum threshold (e.g., where a less than typical or normalleakage current (e.g., I_(C)) is flowing between the output terminals ofthe particular semiconductor switch).

The method of FIG. 6 is similar to the method of FIG. 3, except themethod of FIG. 4 further comprises step S310.

In step S310, the data processor 10 sends a signal to remove directcurrent bus power to the controller upon detection of the fault. Forexample, the data processor 10 sends a control signal to the directcurrent power switch 29 to open to remove power to the direct currentbus.

The method of FIG. 7 is similar to the method of FIG. 3, except themethod of FIG. 4 further comprises step S312.

In step S312, until power to the controller (e.g., inverter) is recycled(e.g. turned off and on), the data processor 10, the driver 12, or both,simultaneously activate counterpart switches of like direct currentinput polarity that are coupled to other phase windings (e.g., 44, 46,48, 21, 22, 23) of the electric motor (e.g., 15 or 45) than theparticular semiconductor switch to prevent damage to the motor, such asthermal damage to one or more motor windings or demagnetization of oneor more permanent magnets in the electric motor (e.g., 15 or 45).

The method of FIG. 8 is similar to the method of FIG. 3, except themethod of FIG. 4 further comprises step S314.

In step S314, the data processor 10 stores one or more of the followingitems in a data storage device 67: a list, file, inverted file,database, look-up table, or data structure of fault conditions,corresponding collector-emitter voltages, and corresponding controlledswitch states for high side and low side of each phase for retrieval fordetermining which switches to activate in response to a detected shortcircuit or fault.

FIG. 9 is an illustrative table of voltage states of semiconductorswitches, corresponding output current for phase output nodes,corresponding faults detected, and corresponding corrective actions. Theillustrative table may be stored as a look-up table, a file, an invertedfile, a relational database, or another data structure in the datastorage device 67. The same illustrative table may be applied, seriallyor, in some cases, simultaneously, to each phase of the inverter circuitor controller (11 or 111). The first column 901 specifies the currentpolarity of the phase output node or at a winding terminal of the motorwinding. The second column 902 specifies a corresponding high side gatecommand or logic level signal applied to a semiconductor switch of agiven phase of the inverter, whereas the third column 903 specifies thelow side gate command or logic level signal applied to a semiconductorswitch of a given phase of the inverter. The fourth column 904 specifiesthe high side collector-emitter voltage (VCE) for a high sidesemiconductor switch, whereas the fifth column 905 specifies the lowside collector-emitter voltage (VCE) for a low side semiconductorswitch. The sixth column 906 specifies the corresponding condition,including any fault or short circuit states of a semiconductor switch orassociated diode coupled to the semiconductor switches output terminals.The seventh column 907 specifies the corresponding response to preventdamage to the controller or the motor. Each row (951, 952, 953, 954,955, 956 and 957) provides a set of corresponding states that areassociated with a respective condition in the sixth column 906, arespective response in the seventh column 907, or both.

In the first column 901, if the normal current polarity is negative (−),the opposite current polarity is positive (+), and vice versa. Althoughthe second column 902 and the third column 903 each specify a gatecommand, a base command may be substituted for the gate command. Thedriver 12 outputs the gate or base commands as previously described.Similarly, the reference to the “IGBT” or insulated gate bipolartransistor may be substituted for another suitable semiconductor deviceor semiconductor switch (e.g., 81, 82, 181, 182, 281, 282).

The method and system is well-suited for detecting a fault or shortcircuit in particular semiconductor switch of the inverter or controllerto prevent damage to the motor connected to the inverter. For example,upon detection of a fault or short circuit in a semiconductor switch,the data processor may activate other semiconductor switches of likedirect current polarity to eliminate or prevent an asymmetric currentflow between two or more phases of the motor that may lead to motordamage or degradation of permanent magnets of the motor.

Having described the preferred embodiment, it will become apparent thatvarious modifications can be made without departing from the scope ofthe invention as defined in the accompanying claims.

The following is claimed:
 1. A method for providing fault protection ofa controller of an electric motor, the method comprising: measuring thecollector-emitter voltage or source-drain voltage for each semiconductorswitch of a controller; determining that a short circuit in a particularsemiconductor switch is present if the measured collector-emittervoltage or source-drain voltage for the particular semiconductor switchis lower than a minimum threshold during a commanded off-state of theparticular semiconductor switch and if an observed current associatedwith the particular semiconductor switch has an opposite polarity from anormal operational polarity; and simultaneously activating counterpartswitches of like direct current input polarity that are coupled to otherphase windings of the electric motor, other than the particularsemiconductor switch, if the short circuit is determined to be present,to protect the motor from damage associated with asymmetric current flowin its windings.
 2. The method according to claim 1 wherein the shortcircuit in the particular semiconductor switch is a high-side switch ofone phase of the controller and wherein the activated counterpartswitches of like direct current input polarity comprise high-sideswitches of the other phase or phases of the output of the controller.3. The method according to claim 1 wherein the short circuit in theparticular semiconductor switch is a low-side switch of one phase of thecontroller and wherein the activated counterpart switches of like directcurrent input polarity comprise low-side switches of other phase orphases of the output of the controller.
 4. The method according to claim1 further comprising: verifying that the short circuit the particularswitch is present where the particular semiconductor switch remains in aclosed state wherein no bias voltage or a quiescent state bias voltageis provided to the base or gate of the particular semiconductor switch.5. The method according to claim 1 further comprising: verifying thatthe short circuit the particular semiconductor switch is present wherethe particular semiconductor switch does not enter into an open state,indicated by a collector-emitter voltage or source-drain voltageexceeding a maximum threshold, wherein no bias voltage or a quiescentstate bias voltage is provided to the base or gate of the particularsemiconductor switch.
 6. The method according to claim 1 furthercomprising: sending a signal to remove direct current bus power to thecontroller upon detection of the fault.
 7. The method according to claim1 further comprising: until power is cycled, simultaneously activatingcounterpart switches of like direct current input polarity that arecoupled to other phase windings of the electric motor, than theparticular semiconductor switch, to prevent thermal data to one or morewindings or demagnetization of one or more permanent magnets in theelectric motor.
 8. The method according to claim 1 wherein theactivating further comprises: storing in a data storage device a list,look-up table, file, inverted file, database or data structure of faultconditions, corresponding collector-emitter voltages, and correspondingcontrolled switch states for high side and the low side of each phasefor retrieval for determining which switches to activate in response toa detected short circuit or fault in the particular semiconductorswitch.
 9. The method according to claim 1 wherein the determiningfurther comprises determining that a short circuit in a particularsemiconductor switch is present if the measured collector-emittervoltage or source-drain voltage for the particular semiconductor switchis lower than a minimum threshold over at least one complete cycle orwaveform of an inverter driver signal.
 10. A system for providing faultprotection of a controller of an electric motor, the system comprising:a first pair of semiconductor switches comprising a high side switch anda low side switch for a first phase of the controller; a second pair ofsemiconductor switches comprising a high side switch and a low sideswitch for a second phase of the controller; a direct current voltagebus coupled to collector and emitter terminals, or source and drainterminals, of the semiconductor switches; a measuring circuit formeasuring the collector-emitter voltage for each semiconductor switch ofthe controller; a data processor for determining that a short circuit ina particular semiconductor switch, among the semiconductor switches, ispresent if the measured collector-emitter voltage or measuredsource-drain voltage for the particular semiconductor switch is lowerthan a minimum threshold during a commanded off-state of the particularsemiconductor switch and if an observed current associated with theparticular semiconductor switch has an opposite polarity from a normaloperational polarity; and a driver, controlled by the data processor,for simultaneously activating one or more counterpart switches of likedirect current input polarity that are coupled to at least one otherphase winding of the electric motor, other than the particularsemiconductor switch, if the short circuit is determined to be present,to protect the motor from asymmetric current flow in its windings. 11.The system according to claim 10 wherein the short circuit in theparticular semiconductor switch is the high side switch of the firstphase of the controller and wherein the one or more activatedcounterpart switches of like direct current input polarity comprises thehigh-side switch of the second phase of the output of the controller.12. The system according to claim 10 wherein the short circuit in theparticular semiconductor switch is a low-side switch of a first phaseand wherein the one or more activated counterpart switches of likedirect current input polarity comprises the low-side switch of thesecond phase of the output of the controller.
 13. The system accordingto claim 10 further comprising: the data processor adapted to verifythat the short circuit the particular switch is present where the switchremains in a closed state wherein no bias voltage or a quiescent statebias voltage is provided to the base or gate of the semiconductorswitch.
 14. The system according to claim 10 further comprising: thedata processor adapted to verify that the short circuit the particularswitch is present where the switch does not enter into an open state,indicated by a collector-emitter voltage exceeding a maximum threshold,wherein no bias voltage or a quiescent state bias voltage is provided tothe base or gate of the semiconductor switch.
 15. The system accordingto claim 10 further comprising: the data processor further comprising acommunications device for sending a control signal to a direct currentpower switch to remove direct current bus power to the controller upondetection of the short circuit or fault.
 16. The system according toclaim 10 further comprising: until power is cycled, the driver, which iscontrolled by the data processor, is adapted to simultaneously activatecounterpart switches of like direct current polarity that are coupled toother phase windings of the electric motor other than the particularsemiconductor switch to prevent damage to the electric motor.
 17. Thesystem according to claim 10 further comprising: a data storage devicefor storing a data structure of respective fault conditions,corresponding collector-emitter voltages, and corresponding controlledswitch states for high side and the low side of each phase for retrievaland use by the logic control circuit for determining which switches toactivate in response to a detected short circuit or fault, where thedata structure comprises at least one of a file, a database, a look-uptable, an inverted file, a group of records, a list, or a chart.
 18. Thesystem according to claim 10 wherein the voltage measuring circuitcomprises a high impedance measuring circuit that is switchably coupledacross terminals of the low side switching semiconductor or thehigh-side switching semiconductor for each phase.
 19. The systemaccording to claim 10 wherein the data processor is adapted to determinethat a short circuit in a particular semiconductor switch is present ifthe measured collector-emitter voltage or source-drain voltage for theparticular semiconductor switch is lower than a minimum threshold, orapproaches zero volts, over at least one complete cycle or waveform ofan inverter driver signal.
 20. The system according to claim 10 furthercomprising: a plurality of current sensors to measure the observedcurrent associated with the particular semiconductor switch, the totalnumber of the current sensors being limited to N−1, where N is equal tothe number of phases of the electric motor; and the data processoradapted to estimate the observed current for one phase output nodewithout one of said plurality of sensors, the estimation executed inaccordance with electrical network analysis.